JP7654780B2 - Secondary battery - Google Patents

Description

This application claims priority to Korean Patent Application No. 10-2021-0049380, filed on April 15, 2021.

The present invention relates to a secondary battery, and more specifically to a secondary battery equipped with a vent member.

Secondary batteries, which can be applied to a variety of products and have excellent electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs). Such secondary batteries are attracting attention as a new energy source that not only dramatically reduces the use of fossil fuels but also is environmentally friendly as no by-products are generated during the energy consumption process, improving energy efficiency.

Secondary batteries that are currently in widespread use include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel metal hydride batteries, and nickel zinc batteries.

A secondary battery generally has a structure in which an electrode assembly including at least one unit cell having a positive electrode/separator/negative electrode structure is housed in a case made of a laminate sheet in which an outer layer, a metal barrier layer, and a sealant layer are laminated in that order, and the electrode assembly is sealed by fusing the sealant resin of the sealant layer.

Conventionally, secondary batteries can catch fire due to a variety of reasons, including short circuits inside the secondary battery, overcharging or over-discharging, and temperature regulation. When this happens, the internal temperature of the secondary battery rises rapidly and at the same time, a thermal propagation phenomenon occurs in which heat is transferred to adjacent cells, which can cause the fire to spread further.

When thermal runaway occurs, i.e. when the internal temperature of a secondary battery rises, a directional venting characteristic that allows gas to be exhausted in one direction is required to minimize damage to the electrodes caused by gas. However, conventional secondary batteries have a problem in that it is difficult to induce gas exhaust in a specific direction.

Therefore, the present invention aims to provide a secondary battery with improved safety by directing gas exhaust in a specific direction.

The problem that this invention aims to solve is to provide a secondary battery with improved safety by directing gas exhaust in a specific direction.

To achieve the above object, according to one aspect of the present invention, a secondary battery of the following embodiment is provided.

The first embodiment is
An electrode assembly;
an electrode lead attached to the electrode assembly;
a case for accommodating the electrode assembly therein;
a lead film formed to cover a part of an outer surface of the electrode lead and interposed between the electrode lead and the case;
a vent area formed in at least a portion of the case;
a vent member that is inserted into the vent region and has a three or more layer structure including a first resin in a bottom layer, a second resin in a top layer, and a third resin in an intermediate layer;
The second resin has a melting point higher than that of the first resin,
The present invention relates to a secondary battery, wherein the third resin has a melting point higher than that of the second resin.

According to the second embodiment, in the first embodiment,
Venting may occur between the middle layer and the bottom layer.

According to a third embodiment, in the first or second embodiment,
The melting point of the first resin may be 90°C or higher and lower than 100°C.

According to a fourth embodiment, in any one of the first to third embodiments,
The first resin may be a linear low density polyethylene having a comonomer having 8 carbon atoms.

According to a fifth embodiment, in any one of the first to fourth embodiments,
The first resin may have a polydispersity index (PDI) of less than 2.6.

According to the sixth embodiment, in the fourth or fifth embodiment,
The content of the comonomer having 8 carbon atoms in the linear low-density polyethylene having a comonomer having 8 carbon atoms may be 12% by weight or more based on 100% by weight of the linear low-density polyethylene having a comonomer having 8 carbon atoms.

According to the seventh embodiment, in any one of the first to sixth embodiments,
The first resin may have a crystallization temperature of 80°C to 90°C.

According to an eighth embodiment, in any one of the first to seventh embodiments,
The first resin may have a weight average molecular weight of 100,000 g/mol to 250,000 g/mol.

According to the ninth embodiment, in any one of the fourth to eighth embodiments,
The linear low density polyethylene having a comonomer having 8 carbon atoms may be polymerized in the presence of a metallocene catalyst.

According to a tenth embodiment, in any one of the first to ninth embodiments,
The case may include a sealing portion formed to seal the electrode assembly, the sealing portion may include a sealant resin, and the linear low-density polyethylene having a comonomer having 8 carbon atoms contained in the vent member may have a melting point lower than that of the sealant resin.

According to an eleventh embodiment, in any one of the first to tenth embodiments,
The melting point of the second resin may be in the range of 100°C to 130°C.

According to a twelfth embodiment, in any one of the first to eleventh embodiments,
The second resin may be a linear low density polyethylene having a comonomer having six or more carbon atoms.

According to a thirteenth embodiment, in any one of the first to twelfth embodiments,
The second resin may have a polydispersity index (PDI) of 2.6 or more and 4 or less.

According to the fourteenth embodiment, in the twelfth or thirteenth embodiment,
The content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be less than 12% by weight, based on 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms.

According to a fifteenth embodiment, in any one of the first to fourteenth embodiments,
The second resin may have a crystallization temperature of more than 90° C. and not more than 115° C.

According to a sixteenth embodiment, in any one of the first to fifteenth embodiments,
The second resin may have a weight average molecular weight of more than 250,000 g/mol and not more than 400,000 g/mol.

According to the seventeenth embodiment, in any one of the twelfth to sixteenth embodiments,
The linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst.

According to an eighteenth embodiment, in any one of the first to seventeenth embodiments,
The melting point of the third resin may be greater than 130°C.

According to the 19th embodiment, in any one of the 1st to 18th embodiments,
The third resin may include high density polyethylene, random polypropylene, or a mixture thereof.

According to the twentieth embodiment, in any one of the first to nineteenth embodiments,
The vent member may melt at 100° C. or higher to release gas.

According to the twenty-first embodiment, in the twenty-first embodiment,
The vent member may be one that vents at a pressure of 1.5 atm or more.

According to the twenty-second embodiment, in any one of the first to twenty-first embodiments,
The vent member may have a maximum sealing strength of less than 6 kgf/15 mm at 100° C. or higher.

According to the twenty-third embodiment, in any one of the first to twenty-second embodiments,
The vent member may have an average sealing strength of less than 4.5 kgf/15 mm at 100° C. or higher.

According to the twenty-fourth embodiment, in any one of the first to twenty-third embodiments,
The vent member may have a maximum sealing strength of 6 kgf/15 mm or more at room temperature to 60°C.

According to the twenty-fifth embodiment, in any one of the first to twenty-fourth embodiments,
The vent member may have an average sealing strength of 4.5 kgf/15 mm or more at room temperature to 60°C.

According to the 26th embodiment, in any one of the 10th to 25th embodiments,
The vent area may be located at the sealing portion.

According to the twenty-seventh embodiment, in the twenty-sixth embodiment,
The vent area may be located at a sealing portion on a corner side of the case.

According to the twenty-eighth embodiment, in any one of the first to twenty-seventh embodiments,
The secondary battery may be a pouch-type secondary battery.

The secondary battery according to one embodiment of the present invention is provided with a vent member having a three or more layer structure including a first resin in the bottom layer, a second resin having a higher melting point than the first resin in the top layer, and a third resin having a higher melting point than the second resin in the middle layer. This not only makes it easier to induce gas discharge to the vent area, but also improves the rigidity of the vent member. This improves the safety of the battery.

The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the detailed description of the invention, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to only the matters described in the drawings.

1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention; 1 is a plan view showing a secondary battery according to an embodiment of the present invention; 4 is a diagram illustrating a state in which venting occurs in a secondary battery according to an embodiment of the present invention; FIG. FIG. 4 is a plan view showing a secondary battery according to another embodiment of the present invention. FIG. 13 is a plan view showing a secondary battery according to still another embodiment of the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Prior to this, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as having meanings and concepts that correspond to the technical ideas of the present invention, in accordance with the principle that the inventor himself can appropriately define the concepts of terms in order to best describe the invention.

Therefore, it should be understood that the embodiment described in this specification and the configuration shown in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of the present invention, and that there may be various equivalents and modifications that can be substituted for them at the time of this application.

A secondary battery according to one embodiment of the present invention includes an electrode assembly having an electrode lead attached thereto, a case housing the electrode assembly therein, a lead film formed to cover a portion of the outer surface of the electrode lead and interposed between the electrode lead and the case, a vent region formed in at least a portion of the case, and a vent member inserted into the vent region and having a three or more layer structure including a first resin in the bottom layer, a second resin in the top layer, and a third resin in the middle layer. In this case, the second resin is a resin having a higher melting point than the first resin, and the third resin is a resin having a higher melting point than the second resin.

Figures 1 and 2 show a secondary battery according to one embodiment of the present invention.

Referring to Figures 1 and 2, the secondary battery 10 comprises an electrode assembly 12 to which an electrode lead 11 is attached, and a case 13.

The electrode assembly 12 includes a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly 12 may include a positive electrode plate and a negative electrode plate stacked in sequence with a separator interposed therebetween.

The positive electrode plate may include a positive electrode collector made of a metal thin plate having excellent conductivity, for example, aluminum (Al) foil, and a positive electrode active material layer coated on at least one surface of the positive electrode collector. The positive electrode plate may also include a positive electrode tab made of a metal material, for example, aluminum (Al) material, at one end. The positive electrode tab may protrude from one end of the positive electrode plate. The positive electrode tab may be welded to one end of the positive electrode plate or bonded using a conductive adhesive.

The negative electrode plate may include a negative electrode collector made of a conductive metal thin plate, for example, copper (Cu) foil, and a negative electrode active material layer coated on at least one surface thereof. The negative electrode plate may also include a negative electrode tab formed of a metal material, for example, nickel (Ni) material, at one end. The negative electrode tab may protrude from one end of the negative electrode plate. The negative electrode tab may be welded to one end of the negative electrode plate or bonded using a conductive adhesive.

The separator is located between the positive and negative electrode plates and electrically insulates the positive and negative electrode plates. The separator may be a porous membrane that allows lithium ions to pass between the positive and negative electrode plates. The separator may include a porous membrane using, for example, polyethylene (PE), polypropylene (PP), or a composite film thereof.

The surface of the separation membrane may be provided with an inorganic coating layer. The inorganic coating layer may have a structure in which inorganic particles are bound to each other by a binder to form a pore structure (interstitial volume) between the particles.

The electrode assembly 12 may be a jelly-roll type (wound-type) electrode assembly in which long sheet-like positive and negative electrodes are wound with a separator interposed therebetween, a stacked type electrode assembly in which a number of positive and negative electrodes cut into units of a predetermined size are stacked in sequence with a separator interposed therebetween, or a stacked/folded type electrode assembly in which a bi-cell or full-cell in which a predetermined number of positive and negative electrodes are stacked with a separator interposed therebetween is wound up.

The case 13 serves to house the electrode assembly 12.

In one embodiment of the present invention, the case 13 may include a storage portion 13a for storing the electrode assembly 12, and a sealing portion 13b formed to seal the electrode assembly 12, as shown in FIG. 1.

The sealing portion 13b may include a sealant resin, which may be fused along the outer circumferential surface of the storage portion 13a to seal the electrode assembly 12.

In one embodiment of the present invention, the case 13 may be provided in the form of a multi-layered film consisting of an outer layer for protection from external impact, a metal barrier layer for blocking moisture, and a sealant layer for sealing the case.

The outer layer may include a polyester-based film using polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, polycarbonate, nylon, etc., and may be constructed as a single layer or multiple layers.

The metal barrier layer may include aluminum, copper, etc.

The sealant layer may contain a sealant resin and may be composed of a single layer or multiple layers.

The sealant resin may include polypropylene (PP), acid modified polypropylene (PPa), random polypropylene, ethylene propylene copolymer, or two or more of these. The ethylene propylene copolymer may include, but is not limited to, ethylene propylene rubber, ethylene-propylene block copolymer, etc.

In one embodiment of the present invention, the case 13 may be pouch-shaped.

The pouch-type battery case 13 may include an upper pouch and a lower pouch. When the case 13 includes an upper pouch and a lower pouch, the upper pouch and the lower pouch are arranged so that the sealant resins face each other, and then the opposing sealant resins are fused to each other by heat and pressure to seal the battery.

The sealing portion 13b can be fused by heat fusion, ultrasonic fusion, etc., but there are no particular limitations as long as the sealing portion 13b can be fused.

In some embodiments, the sealing portion 13b may be four-sided or three-sided sealed around the periphery of the case 13. In a three-sided sealing structure, the upper and lower pouches are formed from a single pouch sheet, and then the boundary between the upper and lower pouches is folded to overlap the storage portions 13a formed in the upper and lower pouches, and the remaining three peripheries excluding the folded portion are sealed.

The electrode lead 11 may be housed in the case 13 such that a portion of the electrode lead 11 is exposed outside the case 13, as shown in FIG. 1.

The secondary battery 10 according to one embodiment of the present invention includes a lead film 14.

The lead film 14 covers a portion of the outer surface of the electrode lead 11 and is interposed between the electrode lead 11 and the case 13. For example, the lead film 14 can be interposed between the electrode lead 11 and the sealing portion 13b of the case 13 at the portion where the electrode lead 11 protrudes or extends from the case 13, thereby assisting in the attachment of the electrode lead 11 to the case 13.

Referring to FIG. 1 and FIG. 2, a secondary battery 10 according to an embodiment of the present invention includes a vent area (not shown) formed in at least a portion of the case 13, and a vent member 15 can be inserted into the vent area. When a thermal runaway phenomenon occurs, the vent member 15 can improve the safety of the battery by inducing gas discharge in a specific direction.

The vent member 15 and the case 13 may be overlapped through thermal fusion. As another example, the vent member 15 and the case 13 may be overlapped through an adhesive such as glue. As yet another example, the vent member 15 and the case 13 may be physically connected through a clip or the like. As yet another example, at least a portion of the vent member 15 may be embedded in a film that constitutes the case 13, for example, a sealant resin.

The vent member 15 has a structure of three or more layers. The vent member 15 contains a first resin in the bottom layer 15a, a second resin in the top layer 15b, and a third resin in the middle layer 15c. The vent member 15 contains resins with different melting points on one side and the other side, so that venting occurs on one side of the vent member 15. This makes it easy to adjust the venting direction in one direction. For example, venting may occur on one side of the vent member 15 that contains the first resin with the lowest melting point.

If the rigidity of the vent member 15 is insufficient, there is a risk that premature venting may occur before the target temperature and pressure conditions when the internal pressure of the battery increases. When the third resin is included, the melting point of the third resin is higher than the melting points of the first resin and the second resin, so that the rigidity of the vent member 15 can be improved compared to when only the first resin and/or the second resin is included. This makes it possible to prevent premature venting from occurring before the target temperature and pressure conditions when the internal pressure of the battery increases.

The vent member 15 has excellent sealing properties for the case 13 in the normal temperature range, for example, room temperature to 60°C, but at high temperatures, for example, above 100°C, the sealing strength of the case into which the vent member 15 is inserted decreases, allowing venting to be realized or induced.

Figure 3 is a diagram showing a state in which venting occurs in a secondary battery according to one embodiment of the present invention. Specifically, Figure 3 is a cross-sectional view showing a vent member included in a secondary battery according to one embodiment of the present invention.

Referring to FIG. 3, at the temperature at which the battery operates normally, the vent member serves to seal the case from the outside. If the temperature of the battery rises excessively due to abnormal operation of the battery, the vent member melts and the sealing strength of the part where the vent member is inserted decreases. Therefore, gas is discharged from this part. For example, the pressure of the internal gas of the battery is applied to the interface between the vent member and the case, forming a gap between the vent member and the case, through which gas can be discharged.

For example, if the battery temperature rises excessively due to abnormal operation of the battery, the first resin contained in the bottom layer 15a, which has a lower melting point than the middle layer 15c and the top layer 15b, melts. As the first resin melts, the sealing strength of the portion where the vent member is inserted decreases. Because the second resin has a higher melting point than the first resin, the bottom layer 15a melts faster than the top layer 15b. This makes it easier for venting to occur on the bottom layer 15a side than the top layer 15b. Because the third resin has a higher melting point than the first and second resins, the middle layer 15c is less likely to melt even if the battery temperature rises.

As shown in FIG. 3, venting may occur between the intermediate layer 15c and the bottom layer 15a. Because the fusion characteristics between the intermediate layer 15c and the bottom layer 15a are inferior to the fusion characteristics between the bottom layer 15a and the case 13, venting may occur between the intermediate layer 15c and the bottom layer 15a.

In one embodiment of the present invention, the vent member 15 may be manufactured by sequentially stacking the first resin, the third resin, and the second resin, and then fusing them together. For example, the first resin, the third resin, and the second resin may be sequentially stacked, and then heat-sealed. As another example, they may be fused together using an adhesive such as glue.

In one embodiment of the present invention, the vent member 15 can vent at 100°C or higher. The vent member 15 can vent sooner than if it contained only the second resin.

In one embodiment of the present invention, the vent member 15 can vent at 100°C or higher, for example, 100°C to 120°C, and can discharge or exhaust gas from the storage section to the outside of the battery. In particular, the vent member 15 can vent at 100°C or higher and a pressure of 1.5 atm or higher. By venting the vent member 15 within the above temperature range and/or the above pressure conditions, the battery can be sealed when the battery is operating normally, and gas can be exhausted only when the battery is operating abnormally.

In one embodiment of the present invention, the vent member 15 may have a lower maximum sealing strength at 100°C or higher than when it contains only the second resin. This allows for earlier venting than when it contains only the second resin.

In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf/15 mm, less than 5 kgf/15 mm, less than 4.5 kgf/15 mm, less than 3 kgf/15 mm, or less than 2.6 kgf/15 mm at 100°C or higher. In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf/15 mm, less than 5 kgf/15 mm, less than 4.5 kgf/15 mm, less than 3 kgf/15 mm, or less than 2.6 kgf/15 mm at 100°C to 120°C. In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 3 kgf/15 mm, less than 2 kgf/15 mm, less than 1 kgf/15 mm, less than 0.5 kgf/15 mm, less than 0.1 kgf/15 mm, or less than 0.05 kgf/15 mm at 120°C or higher. If the vent member 15 meets the above-mentioned sealing strength in the above-mentioned temperature range, the sealing strength of the part of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, 100°C or higher, making it easier to achieve vent characteristics.

In one embodiment of the present invention, the vent member 15 has a higher maximum sealing strength at room temperature to 60°C than when it contains only the second resin. This improves the rigidity of the vent member 15, making it easier to prevent premature venting before the desired temperature and pressure.

In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of 6 kgf/15 mm or more, 8 kgf/15 mm or more, 10 kgf/15 mm or more, or 13 kgf/15 mm or more at room temperature to 60°C. If the vent member 15 meets the above-mentioned sealing strength in the above-mentioned temperature range, even if the vent member 15 is inserted, the part of the case 13 into which the vent member 15 is inserted has excellent sealing strength during normal operation of the battery, and the hermeticity of the battery can be easily ensured.

In one embodiment of the present invention, the vent member 15 may have a maximum sealing strength of less than 6 kgf/15 mm at 100°C or higher, and a maximum sealing strength of 6 kgf/15 mm or higher at room temperature to 60°C. When the vent member 15 satisfies the above-mentioned sealing strength, the sealing strength of the case 13 portion into which the vent member 15 is inserted decreases at high temperatures, for example, 100°C or higher, and vent characteristics can be easily achieved. In addition, when the battery is operating normally, the case 13 has excellent sealing strength, and the hermeticity of the battery can be easily ensured.

In one embodiment of the present invention, the vent member 15 may have an even lower average sealing strength at 100°C or higher than when it contains only the second resin. This allows for earlier venting than when it contains only the second resin.

In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf/15 mm, less than 3 kgf/15 mm, or less than 2.1 kgf/15 mm at 100°C or higher. In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf/15 mm, less than 3 kgf/15 mm, or less than 2.1 kgf/15 mm at 100°C to 120°C. In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 2 kgf/15 mm, less than 1 kgf/15 mm, less than 0.5 kgf/15 mm, less than 0.1 kgf/15 mm, or less than 0.05 kgf/15 mm at 120°C or higher. If the vent member 15 meets the above-mentioned sealing strength in the above-mentioned temperature range, the sealing strength of the part of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, 100°C or higher, making it easier to achieve vent characteristics.

In one embodiment of the present invention, the vent member 15 may have an improved average sealing strength at room temperature to 60°C compared to when it contains only the second resin. This improves the rigidity of the vent member 15, making it easier to prevent premature venting before the desired temperature and pressure.

In one embodiment of the present invention, the vent member 15 may have an average sealing strength of 4.5 kgf/15 mm or more, 5 kgf/15 mm or more, 6 kgf/15 mm or more, 7 kgf/15 mm or more, or 8 kgf/15 mm or more at room temperature to 60°C. If the vent member 15 satisfies the above-mentioned sealing strength in the above-mentioned temperature range, even if the vent member 15 is inserted, the part of the case 13 into which the vent member 15 is inserted has excellent sealing strength during normal operation of the battery, and the hermeticity of the battery can be easily ensured.

In one embodiment of the present invention, the vent member 15 may have an average sealing strength of less than 4.5 kgf/15 mm at 100°C or higher, and an average sealing strength of 4.5 kgf/15 mm or higher at room temperature to 60°C. When the vent member 15 has the above-mentioned sealing strength in the above-mentioned temperature range, the sealing strength of the case 13 portion into which the vent member 15 is inserted decreases at high temperatures, for example, 100°C or higher, and vent characteristics can be easily achieved. In addition, the case 13 has excellent sealing strength during normal operation of the battery, and the hermeticity of the battery can be easily ensured.

The sealing strength of the vent member 15 according to temperature can be measured by cutting the part of the case 13 where the vent member 15 is inserted to a width of 15 mm and a length of 5 cm, opening both ends 180°, fixing them to a UTM jig, and conducting a tensile test at a speed of 5 mm/min.

In this case, the maximum sealing strength means the maximum value at which the case 13 breaks. In addition, the average sealing strength means the average value when the case 13 is stretched by 8 mm at 4.5 kgf/15 mm if the maximum sealing strength is 4.5 kgf/15 mm or more, and means the average value when the case 13 is stretched by 8 mm at the maximum sealing strength if the maximum sealing strength is less than 4.5 kgf/15 mm.

In one embodiment of the present invention, the melting point of the first resin may be less than 100°C. For example, the melting point of the first resin may be 90°C or more and less than 100°C, 90°C to 99°C, or 95°C to 99°C. When the melting point of the first resin satisfies the above-mentioned range, the sealing strength of the part of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example 100°C or more, and venting characteristics can be achieved more easily. In particular, venting is possible earlier than when only the second resin is included.

Even if the melting point of the first resin is less than 100°C, it is used in the vent member 15 together with other resins that can complement it, making venting at high temperatures easier and improving the rigidity of the vent member 15. For example, when the battery is operating normally, the part of the case 13 into which the vent member 15 is inserted has excellent sealing strength, making it easy to ensure the hermeticity of the battery.

In this specification, the melting point of the resin may be measured using a differential scanning calorimeter (DSC). For example, the temperature of the sample may be increased from 30°C to 280°C at 10°C/min, maintained at 280°C for 10 minutes, cooled to 30°C at 10°C/min, and maintained at 30°C for 10 minutes. The temperature of the sample may then be increased from 30°C to 280°C at 10°C/min, and maintained at 280°C for 10 minutes to measure the melting point.

In one embodiment of the present invention, the polydispersity index (PDI) of the first resin may be less than 2.6, 2.59 or less, or 2.551 or less. The polydispersity index (PDI) of the first resin may be 1 or more. Venting may occur more easily in the bottom layer of the vent member containing the first resin.

In one embodiment of the present invention, the weight average molecular weight of the first resin may be 100,000 g/mol to 250,000 g/mol, 150,000 g/mol to 250,000 g/mol, or 180,000 g/mol to 220,000 g/mol. When the weight average molecular weight of the first resin satisfies the above range, the first resin is likely to have a low melting point, for example, a melting point less than 100°C, and therefore the sealing strength of the vent member is likely to be further reduced at high temperatures, for example, 100°C or higher, making it easy to induce early venting.

In this specification, the weight average molecular weight and polydispersity index of the resin may be measured using gel permeation chromatography (GPC) under the following conditions:

- Column: Tosoh Corporation, HLC-8321 GPC/HT
- Solvent: TCB (trichlorobenzene) + 0.04% BHT (dried with 0.1% _CaCl2 )
- Flow rate: 1.0 ml/min - Sample concentration: 1.5 mg/ml
Injection volume: 300 μl
- Column temperature: 160 ° C.
- Detector: RI detector - Standard: polystyrene (corrected with a cubic function)

In one embodiment of the present invention, the crystallization temperature of the sealant resin and the crystallization temperature of the first resin may be significantly different. For example, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin may be 20°C or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin satisfies the above-mentioned range, venting can occur more easily in the bottom layer of the vent member containing the first resin.

In one embodiment of the present invention, the crystallization temperature of the first resin may be 80°C to 90°C, or 80°C to 85°C. When the crystallization temperature of the first resin satisfies the above-mentioned range, venting can occur more easily in the bottom layer of the vent member containing the first resin. In one embodiment of the present invention, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the first resin is 20°C or more, and the crystallization temperature of the first resin may be 80°C to 90°C.

In this specification, the crystallization temperature may be measured using a differential scanning calorimeter (DSC). For example, the temperature of the sample may be increased from 30°C to 280°C at 10°C/min, then maintained at 280°C for 10 minutes, cooled to 30°C at 10°C/min, and maintained at 30°C for 10 minutes. The temperature of the sample may then be increased from 30°C to 280°C at 10°C/min, then maintained at 280°C for 10 minutes to measure the crystallization temperature.

In one embodiment of the present invention, the first resin may be linear low-density polyethylene having a comonomer with 8 carbon atoms. When the first resin is linear low-density polyethylene having a comonomer with 8 carbon atoms, the sealing strength of the case into which the vent member 15 is inserted is likely to decrease at high temperatures, for example, 100°C or higher.

In one embodiment of the present invention, the content of the C8 comonomer in the linear low density polyethylene having a C8 comonomer may be 12 wt% or more, 12 wt% to 20 wt%, or 12 wt% to 18 wt%, based on 100 wt% of the linear low density polyethylene having a C8 comonomer. When the content of the C8 comonomer satisfies the above range, venting may occur more easily in the bottom layer of the vent member including the first resin. In this specification, the comonomer content may be measured by H-NMR. For example, about 10 mg of a sample may be completely dissolved in about 0.6 mL of trichloroethylene solvent using a heat gun, and then the sample may be sampled in an NMR tube and measured using ¹ H-NMR.

In one embodiment of the present invention, the linear low-density polyethylene having a comonomer with 8 carbon atoms may be polymerized in the presence of a metallocene catalyst. When the linear low-density polyethylene having a comonomer with 8 carbon atoms is polymerized in the presence of a metallocene catalyst, it is more advantageous in terms of sealing strength and physical properties than when it is polymerized in the presence of a Ziegler-Natta catalyst.

In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a melting point of less than 100°C and a comonomer having 8 carbon atoms. In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a polydispersity index (PDI) of less than 2.6 and a comonomer having 8 carbon atoms. In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a crystallization temperature of 80°C to 90°C and a comonomer having 8 carbon atoms. In one embodiment of the present invention, the first resin may be a linear low-density polyethylene having a weight average molecular weight of 100,000 g/mol to 250,000 g/mol and a comonomer having 8 carbon atoms.

In one embodiment of the present invention, the first resin may have a lower melting point than the sealant resin. If the melting point of the first resin is lower than that of the sealant resin, the first resin may melt faster than the sealant resin at high temperatures. As a result, the sealing strength of the portion into which the vent member 15 is inserted is further reduced compared to the sealing strength of the case portion containing the sealant resin, making it easier to achieve vent characteristics.

In one embodiment of the present invention, the melting point of the second resin may be 100°C to 130°C, 105°C to 130°C, 110°C to 125°C, or 115°C to 125°C. When the melting point of the second resin is within the above-mentioned range, the sealing strength of the part of the case 13 into which the vent member 15 is inserted decreases at high temperatures, for example, 100°C or higher, making it easier to achieve vent characteristics.

In one embodiment of the present invention, the polydispersity index (PDI) of the second resin may be 4 or less, 3.8 or less, 3.796 or less, 3.5 or less, 3.023 or less, 3 or less, 2.7 or less, or 2.674 or less. The polydispersity index may be 2.6 or more. When the polydispersity index of the second resin satisfies the above range, the molecular weight distribution is narrow, and therefore the battery exhibits better sealing strength and physical properties during normal operation.

In one embodiment of the present invention, the weight average molecular weight of the second resin may be more than 250,000 g/mol and less than 400,000 g/mol, 200,000 g/mol to 350,000 g/mol, or 230,000 g/mol to 300,000 g/mol. When the weight average molecular weight of the second resin satisfies the above range, the sealing strength during normal operation of the battery may be further improved.

In one embodiment of the present invention, the crystallization temperature of the sealant resin and the crystallization temperature of the second resin may be similar. For example, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin may be 10°C or less, or 5°C or less. Also, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin may be 0.1°C or more. When the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin satisfies the above-mentioned range, the fusion characteristics of the sealant resin and the second resin are more excellent during normal operation of the battery.

In one embodiment of the present invention, the crystallization temperature of the second resin may be greater than 90°C and less than 115°C, 95°C to 110°C, 100°C to 110°C, or 105°C to 110°C. When the crystallization temperature of the second resin satisfies the above-mentioned range, the fusion properties between the sealant resin and the second resin are more excellent.

In one embodiment of the present invention, the difference between the crystallization temperature of the sealant resin and the crystallization temperature of the second resin is 10°C or less, and the crystallization temperature of the second resin may be greater than 90°C and less than 115°C.

In one embodiment of the present invention, the second resin may be linear low density polyethylene having a comonomer with 6 or more carbon atoms. When the second resin is linear low density polyethylene having a comonomer with 6 or more carbon atoms, the case 13 has excellent sealing properties in the normal temperature range, for example, room temperature to 60°C, and at high temperatures, for example, 100°C or higher, the sealing strength of the case into which the vent member 15 is inserted decreases, thereby realizing or inducing venting. For example, the second resin may include linear low density polyethylene having a comonomer with 6 to 8 carbon atoms.

In one embodiment of the present invention, the content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be less than 12 wt%, 11.8 wt% or less, 10 wt% or less, 9 wt% or less, 8 wt% or less, or 7.6 wt% or less, based on 100 wt% of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. The content of the comonomer having 6 or more carbon atoms may be 5 wt% or more, 7.6 wt% or more, 8 wt% or more, 9.0 wt% or more, 10 wt% or more, or 11.8 wt% or more, based on 100 wt% of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. When the content of the comonomer having 6 or more carbon atoms satisfies the above-mentioned range, the problem of the intermolecular packing density decreasing and the sealing strength decreasing during normal operation of the battery can be easily prevented.

In one embodiment of the present invention, the linear low-density polyethylene having a comonomer having 6 or more carbon atoms may be polymerized in the presence of a metallocene catalyst. When the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is polymerized in the presence of a metallocene catalyst, it is more advantageous in terms of sealing strength and physical properties than when it is polymerized in the presence of a Ziegler-Natta catalyst.

In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a melting point of 100°C to 130°C and a comonomer having 6 or more carbon atoms. In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a polydispersity index (PDI) of 2.6 to 4 and a comonomer having 6 or more carbon atoms. In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a crystallization temperature of more than 90°C to 115°C and a comonomer having 6 or more carbon atoms. In one embodiment of the present invention, the second resin may be a linear low-density polyethylene having a weight average molecular weight of more than 250,000 g/mol to 400,000 g/mol and a comonomer having 6 or more carbon atoms.

In one embodiment of the present invention, the second resin may have a lower melting point than the sealant resin. This makes it easier to induce venting at high temperatures.

In one embodiment of the present invention, the melting point of the third resin may be greater than 130°C, between 131°C and 140°C, or between 132°C and 138°C. When the melting point of the third resin is within the above-mentioned range, the rigidity of the vent member 15 can be more easily improved.

In one embodiment of the present invention, the crystallization temperature of the first resin may be significantly different from the crystallization temperature of the third resin. For example, the difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin is greater than the difference between the crystallization temperature of the first resin and the crystallization temperature of the sealant resin, and the fusion characteristics of the third resin and the first resin are inferior to the fusion characteristics of the first resin and the sealant resin. Therefore, venting can occur more easily at the interface between the intermediate layer containing the third resin and the bottom layer of the vent member containing the first resin than at the interface between the first resin and the sealant resin.

In one embodiment of the present invention, the difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin may be 30° C. or more. When the difference between the crystallization temperature of the first resin and the crystallization temperature of the third resin satisfies the above-mentioned range, venting can occur more easily between the middle layer containing the third resin and the bottom layer of the vent member containing the first resin.

In one embodiment of the present invention, the crystallization temperature of the third resin may be greater than 115°C. For example, the crystallization temperature of the third resin may be 116°C to 130°C, or 116°C to 120°C. When the crystallization temperature of the third resin satisfies the above-mentioned range, venting can occur more easily between the middle layer containing the third resin and the bottom layer of the vent member containing the first resin.

In one embodiment of the present invention, the difference between the crystallization temperature of the third resin and the crystallization temperature of the first resin may be 30°C or more, and the crystallization temperature of the third resin may be greater than 115°C.

In one embodiment of the present invention, the third resin may include high density polyethylene, random polypropylene, or a mixture thereof.

In one embodiment of the present invention, the vent member 15 may have a variety of shapes to allow gas to flow smoothly to the vent area. For example, the vent member 15 may have a film shape.

The vent member 15 can be formed to have a predetermined thickness.

In one embodiment of the present invention, as shown in Figures 1 and 2, the vent member 15 may be located in the sealing portion.

Referring to FIG. 2, the vent member 15 may be located in the sealing portion at the corner side of the case. For example, the vent member 15 may be located at the corner side of the sealing portion where the electrode leads 11 are exposed to the outside. Specifically, the vent member 15 may be located in the sealing portion close to the electrode leads 11, except for the areas between the electrode leads 11. When the vent member 15 is located at the corner side of the sealing portion where the electrode leads 11 are exposed to the outside, the amount of gas discharged toward the electrode leads 11 can be minimized, further improving the safety of the battery.

In one embodiment of the present invention, when the sealing portion 13b is sealed on three sides, the folded side of the case and one end of the vent member 15 can be in close contact with each other.

Also, the vent member 15 can be inserted into the case 13 to vary the insertion length or to control the venting pressure and position depending on the design. Here, the insertion length of the vent member means the maximum distance between one end and the other end of the vent member based on the protruding direction of the electrode lead.

In one embodiment of the present invention, the insertion length of the vent member 15 may be smaller than the width of the sealing portion 13b. For example, the insertion length of the vent member 15 may be less than about 50% of the width of the sealing portion 13b. Here, the width of the sealing portion 13b refers to the maximum distance between one end and the other end of the sealing portion 13b based on the protruding direction of the electrode lead 11.

In other embodiments of the present invention, the insertion length of the vent member 15 may be greater than the width of the sealing portion 13b. For example, the vent member 15 may be inserted through the storage portion 13a so as to be exposed to the outside of the case 13.

In one embodiment of the present invention, the vent member 15 may further include an adhesive layer for smoother placement.

Figure 4 is a plan view showing a secondary battery according to another embodiment of the present invention.

Referring to FIG. 4, the vent member 15 may be located in the sealing portion except for the sealing portion where the electrode lead 11 is exposed to the outside.

Figure 5 is a plan view showing a secondary battery according to yet another embodiment of the present invention.

Referring to FIG. 5, the vent member 15 may be located in a sealing portion where the electrode leads 11 are exposed to the outside. For example, the vent member 15 may be located in a sealing portion between the electrode leads 11.

The secondary battery according to one embodiment of the present invention includes a vent member having a three or more layer structure including a first resin in the bottom layer, a second resin in the top layer, and a third resin in the middle layer, which reduces the sealing strength at high temperatures and allows for smoother and faster directional venting that can release gas in a specific direction, and minimizes damage to electrodes caused by gas when a thermal runaway phenomenon occurs, i.e., when the internal temperature of the secondary battery rises. In addition, the rigidity of the vent member is improved, which prevents premature venting before the desired temperature and pressure are reached.

In one embodiment of the present invention, the secondary battery may be a cylindrical, rectangular, or pouch-type secondary battery. In particular, the secondary battery may be a pouch-type secondary battery.

The present invention will now be described in detail with reference to specific examples. However, the examples of the present invention may be modified into many other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1
A linear low-density polyethylene having a thickness of 50 μm and a comonomer having a carbon number of 6 polymerized in the presence of a metallocene catalyst (Lucene™, SP311, manufactured by LG Chemical) (melting point: 119° C., comonomer content relative to the total resin content: 9 wt%, weight average molecular weight: 270,756 g/mol, polydispersity index: 2.674, crystallization temperature: 107° C.) was laminated on one side of a high-density polyethylene having a thickness of 50 μm and a comonomer having a carbon number of 8 polymerized in the presence of a metallocene catalyst (Sabic (registered trademark), ^HDPE F04660, melting point: 135° C., weight average molecular weight: 350,000 g/mol, crystallization temperature: 119° C.). A linear low-density polyethylene having a thickness of 50 μm and a comonomer having a carbon number of 8 polymerized in the presence of a metallocene catalyst (Lucene™, manufactured by LG Chemical) (melting point: 119° C., comonomer content relative to the total resin content: 9 wt%, weight average molecular weight: 270,756 g/mol, polydispersity index: 2.674, crystallization temperature: 107° C. ⁾ was laminated on the other side of the high-density polyethylene. LF100) (melting point: 99°C, comonomer content relative to total resin content: 16.3 wt%, weight average molecular weight: 205,603 g/mol, polydispersity index: 2.551, crystallization temperature: 83°C) were laminated, heat-sealed at 100°C, and cut to a width of 100 mm to manufacture a vent member.

The upper and lower pouches, each made of polyethylene terephthalate/aluminum foil/polypropylene resin stacked in that order, were placed so that the polypropylene resins faced each other, and then an electrode assembly made of a positive electrode/separator/negative electrode stacked in that order was placed inside.

Then, the manufactured vent member was inserted between the polypropylene resin and heat-sealed at 200°C and 0.08 MPa for 1.5 seconds to manufacture a secondary battery.

Comparative Example 1
An upper pouch and a lower pouch in which polyethylene terephthalate/aluminum foil/polypropylene resin were laminated in this order were arranged so that the polypropylene resins faced each other, and then an electrode assembly in which a positive electrode/separator/negative electrode were laminated in this order was housed inside the pouch.

The polypropylene resin was then heat fused to produce a secondary battery.

Comparative Example 2
An upper pouch and a lower pouch in which polyethylene terephthalate/aluminum foil/polypropylene resin were laminated in this order were arranged so that the polypropylene resins faced each other, and then an electrode assembly in which a positive electrode/separator/negative electrode were laminated in this order was housed inside the pouch.

Then, a vent member made of linear low-density polyethylene having a carbon number of 6 comonomer polymerized in the presence of a metallocene catalyst (Lucene ^™ , SP311, manufactured by LG Chem) having a thickness of 50 μm (melting point: 119° C., comonomer content relative to total resin content: 9 wt%, weight average molecular weight: 270,756 g/mol, polydispersity index: 2.674, crystallization temperature: 107° C.) was inserted between the polypropylene resin, and then heat-sealed for 1.5 seconds at 200° C. and 0.08 MPa to manufacture a secondary battery.

Evaluation Example 1: Measurement of sealing strength according to temperature Using the secondary batteries manufactured in Example 1 and Comparative Example 2, the case where the vent member was inserted was cut to a width of 15 mm and a length of 5 cm at the following temperatures, and then both ends were opened 180° and fixed to a UTM jig, and a tensile test was performed at a speed of 5 mm/min. The sealing strength of the case at this time is shown in Table 1 below.

Using the secondary battery manufactured in Comparative Example 1, the sealing part of the case was cut to a width of 15 mm and a length of 5 cm at the following temperature, and then both ends were opened 180° and fixed to a UTM jig, and a tensile test was performed at a speed of 5 mm/min. The sealing strength of the case at this time is shown in Table 1 below.

In this case, the maximum sealing strength means the maximum value at which the case breaks. In addition, the average sealing strength means the average value when the case stretches by 8 mm at 4.5 kgf/15 mm if the maximum sealing strength is 4.5 kgf/15 mm or more, and means the average value when the case stretches by 8 mm at the maximum sealing strength if the maximum sealing strength is less than 4.5 kgf/15 mm.

From Table 1, it can be seen that the maximum sealing strength and average sealing strength at room temperature to 60°C of the case part into which the vent member is inserted in the secondary battery manufactured in Example 1 are higher than the maximum sealing strength and average sealing strength at room temperature to 60°C of the case part into which the vent member is inserted in the secondary battery manufactured in Comparative Example 2. This improves the rigidity of the vent member 15 compared to when it contains only the second resin, making it possible to prevent premature venting before the target temperature and pressure.

In addition, it can be seen that the maximum sealing strength and average sealing strength at 100°C or higher of the case part into which the vent member is inserted in the secondary battery manufactured in Example 1 is lower than the maximum sealing strength and average sealing strength at 100°C or higher of the case part into which the vent member is inserted in the secondary battery manufactured in Comparative Example 2. As a result, the secondary battery manufactured in Example 1 is easier to vent when the battery becomes hot due to an abnormal phenomenon, compared to the secondary battery manufactured in Comparative Example 2.

The secondary battery manufactured in Comparative Example 1 has a maximum sealing strength and average sealing strength of the case at room temperature to 60°C that are similar to the maximum sealing strength and average sealing strength at room temperature to 60°C of the case part where the vent member is inserted in the secondary battery manufactured in Example 1. However, the maximum sealing strength and average sealing strength at 100°C or higher are significantly higher than the maximum sealing strength and average sealing strength at 100°C or higher of the case part where the vent member is inserted in the secondary battery manufactured in Example 1. If the battery becomes hot due to an abnormal phenomenon, gas may be discharged in an unspecified direction, which may cause a chain reaction fire of the battery.

REFERENCE SIGNS LIST 10 secondary battery 11 electrode lead 12 electrode assembly 13 case 13a storage section 13b sealing section 14 lead film 15 vent member 15a bottom layer 15b top layer 15c intermediate layer

Claims (23)

An electrode assembly;
an electrode lead attached to the electrode assembly;
a case that houses the electrode assembly therein and has a sealing portion formed to seal the electrode assembly;
a lead film formed to cover a part of an outer surface of the electrode lead and interposed between the electrode lead and the case;
a vent region formed in at least a part of the sealing portion of the case other than a portion where the lead film is interposed;
a vent member that is inserted into the vent region and has a three or more layer structure including a first resin in a bottom layer, a second resin in a top layer, and a third resin in an intermediate layer;
The first resin is a resin having a lower melting point than a sealant resin of the sealing portion,
The melting point of the first resin is 90° C. or more and less than 100° C.,
The second resin has a melting point higher than that of the first resin,
The third resin has a higher melting point than the second resin. The secondary battery according to claim 1, in which venting occurs between the intermediate layer and the bottom layer. The secondary battery according to claim 1, wherein the first resin is a linear low-density polyethylene having a comonomer having 8 carbon atoms. The secondary battery according to claim 1, wherein the polydispersity index of the first resin is less than 2.6. 4. The secondary battery according to claim 3, wherein a content of the comonomer having 8 carbon atoms in the linear low-density polyethylene having a comonomer having 8 carbon atoms is 12% by weight or more relative to 100% by weight of the linear low-density polyethylene having a comonomer having 8 carbon atoms. The secondary battery according to claim 1, wherein the crystallization temperature of the first resin is 80°C to 90°C. The secondary battery according to claim 1, wherein the weight average molecular weight of the first resin is 100,000 g/mol to 250,000 g/mol. The secondary battery according to claim 1, wherein the melting point of the second resin is 100°C to 130°C. The secondary battery according to any one of claims 1 to 8 , wherein the second resin is a linear low-density polyethylene having a comonomer having six or more carbon atoms. The secondary battery according to claim 1, wherein the polydispersity index of the second resin is 2.6 or more and 4 or less. 10. The secondary battery according to claim 9, wherein a content of the comonomer having 6 or more carbon atoms in the linear low-density polyethylene having a comonomer having 6 or more carbon atoms is less than 12% by weight relative to 100% by weight of the linear low-density polyethylene having a comonomer having 6 or more carbon atoms. The secondary battery according to claim 1, wherein the crystallization temperature of the second resin is greater than 90°C and less than or equal to 115°C. The secondary battery according to claim 1, wherein the weight average molecular weight of the second resin is more than 250,000 g/mol and not more than 400,000 g/mol. The secondary battery according to claim 1, wherein the melting point of the third resin is greater than 130°C. The secondary battery according to claim 1, wherein the third resin includes high-density polyethylene, random polypropylene, or a mixture thereof. The secondary battery according to claim 1, in which the vent member melts at 100°C or higher to release gas. The secondary battery according to claim 16 , wherein the vent member vents at a pressure of 1.5 atm or more. The secondary battery according to claim 1, wherein the maximum sealing strength of the vent member at 100°C or higher is less than 6 kgf/15 mm. The secondary battery according to claim 1, wherein the average sealing strength of the vent member at 100°C or higher is less than 4.5 kgf/15 mm. The secondary battery according to claim 1, wherein the maximum sealing strength of the vent member at room temperature to 60°C is 6 kgf/15 mm or more. The secondary battery according to claim 1, wherein the average sealing strength of the vent member at room temperature to 60°C is 4.5 kgf/15 mm or more. The secondary battery according to claim 1, wherein the vent area is located in a sealing portion on a corner side of the case. The secondary battery according to claim 1, wherein the secondary battery is a pouch-type secondary battery.

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